A number of different ways for disposing of waste have been used extensively. Landfilling and incineration are the major ones, which however, do not seem to offer the best solution.
Landfilling is becoming less and less desirable since it does not offer elimination of waste, but just underground storage. Thus, it has started to be used more for by-products of other types of waste management, such as incineration for example, than for landfilling the primary waste.
Incineration, requiring oxidation of waste at high temperatures with high volumes of air, followed by separation of the effluent gases from the produced ash and the entrained particulate matter, becomes involved, complicated, and expensive, despite the fact that at first glance it sounds to be a simple process of "just burning the waste".
In recent years, a new method, based on supercritical water oxidation, has started being developed. The new method achieves substantially complete oxidation of waste by using considerably more compact equipment, thus becoming an excellent candidate for elimination of waste, even on site. Supercritical water oxidation also has the advantage of producing a clean water product suitable for process recycle, thereby facilitating waste minimization. In addition, it has the advantage of converting spent, costly catalysts (e.g., noble metals in both inorganic and organically bound compounds) to forms which may be more easily recovered, thereby facilitating both waste minimization and cost reduction. However, as with the development of any new process or equipment, there are numerous problems which have not been resolved so far, and which are vital for a finally successful use and commercial exploitation.
In a water liquid/vapor phase diagram, one may see that there is a critical point of temperature (about 720.degree. F.) and a critical point of pressure (about 3,200 psia) over which there is only one single fluid phase.
Although the single phase represents neither liquid nor vapor, it behaves and seems to have more of a gas character than of a liquid one at pressures near the critical pressure. As pressure is raised, a more liquid like behavior is observed, including higher solubility of inorganic matter. The single-phase condition occurring above the critical points is called supercritical condition.
It is worth noting that organic matter decomposes readily under supercritical conditions, and, in the presence of oxygen, carbonaceous compounds oxidize completely to carbon dioxide, sulfur compounds mostly to SO.sub.3 and nitrogen compounds decompose mostly to molecular nitrogen. It is worth noting that under supercritical water oxidation conditions, only small amounts of nitrogen oxides are produced, if any, in contrast with incineration which favors the production of nitrogen oxides. Inorganic salts are substantially insoluble in the supercritical water single phase for pressures of the order of 4,000 psia, while it has been reported that they are at least partially soluble at considerably higher pressures, such as 10,000 psia, for example.
The use of very high pressures at elevated temperatures presents a serious problem in the construction of reactors which can withstand these adverse conditions. It is well known that as the temperature increases the strength of materials decreases drastically. Supercritical pressures (greater than about 3,200 psia) at temperatures exceeding about 1,000.degree. F. present an enormous challenge to any construction material, let alone higher pressures (of the order of 10,000 psia) and temperatures, which may be desirable for a number of reasons, including dissolution of inorganic salts in the supercritical single phase. If in addition to the temperature/pressure challenge, one considers the harsh environment inside the reactor, the problem tends to become unsurmountable.
In order to compromise with this highly undesirable situation, excessively elongated reactors of accordingly small diameter have been practically utilized so far. These conventional reactors, however, have a number of disadvantages which include, but are not limited to restrictions on waste feed materials to preclude corrosive feeds and products of destruction, increased plugging potential due to small diameters, waste feed rate restrictions, increased safety hazards, increased investment cost, and safety hazards, as it will be discussed later, in contrast to the reactor according to this invention.
A number of patents have been dealt in general with supercritical water oxidation of coal, organic substances, and waste, among which are U.S. Pat. Nos. 4,141,829 (Thiel et al.), 4,292,953 (Dickinson), 4,338,199 (Modell), 4,377,066 (Dickinson), 4,380,960 (Dickinson), 4,543,190 (Modell), 4,564,458 (Burleson), 4,593,202 (Dickinson), 4,594,164 (Titmas), 4,792,408 (Titmas), 4,822,394 (Zeigler et al.), 4,822,497 (Hong et al.), 4,861,497 (Welch et al.), 4,891,139 (Zeigler et al.), 5,075,017 (Hossain et al.), 4,113,446 (Modell et al.), 4,338,199 Reexamined (Modell), 5,106,513 (Hong), 4,898,107 (Dickinson), 4,983,296 (McMahon et al.), 5,011,614 (Gresser et al), 5,053,142 (Sorensen et al.), 5,057,231 (Mueller et al.), 5,106,513 (Hong), 5,133,877 (Rofer et al.), 5,183,577 (Lehmann), 5,192,453 (Keckler et al.), 5,221,486 (Fassbender), 5,232,604 (Swallow et al.), 5,232,605 (Baur et al.), 5,240,619 (Copa et al.), 5,250,193 (Sawicki et al.), and 5,252,224 (Modell et al.) all of which are hereby incorporated by reference.
U.S. Pat. No. 3,472,632 (Hervert et al) discloses an internally lined reactor comprising an external pressure retaining chamber, an intermediate porous metal layer within the chamber, and a continuous metal liner positioned along the inner wall of the porous layer. A metal casing encompasses and is spaced from the external chamber. Partitions divide the space between chamber and casing into a number of separate compartments encompassing the chamber. A number of spaced apart leakage passageways are extended through and distributed over the surface of the chamber, and at least one monitoring passageway for each compartment is provided through the casing.
U.S. Pat. No. 3,515,520 (Hervert) discloses a reactor for accommodating corrosive materials wherein a corrosion liner is suspended within an outer reaction chamber and in a non-contacting relationship therewith, the chamber having an inlet for non-corrosive gases at its lower end admitting such gases to the annular space between liner and chamber with a passageway at the top of the liner for admission of such gases, and an adjacent corrosive fluid inlet into the liner with centrally disposed discharge means from said liner for exit of reaction products of the corrosive and non-corrosive gases.
U.S. Pat. No. 4,199,545 (Matovich) discloses a fluid-wall reactor for high temperature chemical reactions comprising (A) a porous reactor tube made of fabric or fibrous refractory material and defining a reaction zone; (B) a pressure vessel enclosing the reactor tube to define an inert fluid plenum, the pressure vessel having at least one inlet for admitting the inert fluid which is directed under pressure through the porous tube wall to provide a protective blanket for the inside surface for the inside surface of the reactor tube; (C) means for introducing at least one reactant into the reaction zone; (D) means in the plenum for heating the reactor tube; and (E) a heat shield disposed within the pressure vessel, substantially enclosing the heating means and the reaction zone to define a black body cavity, the heat shield reflecting radiant energy toward the reaction zone.
U.S. Pat. No. 4,643,890 (Schramm) discloses a reactor tube for a high-temperature fluid wall reactor made of refractory material which permits the tube to be heated to incandescence. The reactor tube in turn radiates energy inwardly to a reaction zone to sustain the desired high-temperature reaction. At least part of the tube is perforated to permit an inert gas to form a protective fluid wall for preventing the reactant products from contacting the inner surface of the tube.
U.S. Pat. No. 4,737,348 (Levin) discloses a reactor apparatus for continuously producing molten, solar grade purity elemental silicon by thermal reaction of a suitable precursor gas, such as silane.
U.S. Pat. No. 5,186,910 (Alagy et al.) discloses an oxidation reactor having an elongated shape and including in combination, a mixing member having a pipe for feeding oxidizing gas and a pipe for feeding oxidizable charge; a reaction member, arranged subjacent the mixing member; and a discharge member associated with a discharge pipe for the products of the reaction. The reaction member includes a central zone which has a first lining and the reactor includes at least one peripheral zone, which has a second lining, passages in the second lining being smaller than passages in the first lining so that the pressure loss in the second lining is greater than that of the first lining. The second lining forms a sleeve surround the first lining and this sleeve is formed of at least one refractory heat insulating material. The oxidation reactor is provided with an external sleeve steel jacket, a concrete wall and a steel element surrounding the mixing member arranged above the reaction member. The reaction member includes a series of single elements which form juxtaposed channels.
U.S. Pat. No. 5,225,169 (Elvin et al. ) discloses an improved sulfider for receiving high temperature catalysts from a hydrocarbon cracking operation and subjecting the catalyst to a sulfur-containing gas. The treating unit includes an outer metal housing and firs refractory layer within the metal housing for minimizing heat loss from the treatment unit. A second refractory layer is provided within the firs refractory layer and defines an interior chamber within the treatment unit, and a plurality of heating units are spaced circumferentially along the interface of the first and second refractory layers. The heating units substantially minimize the temperature differential across the second refractory layer and thereby minimize the heat loss from the high temperature catalyst within the chamber.
None of the above references has resolved the vital problem of pressure/temperature/harsh-environment in a satisfactory manner, and especially under supercritical water conditions.
Our co-pending applications Ser. No. 08/188,229, filed on Jan. 27, 1994, and Ser. No. 08/260,954, filed on Jun. 16, 1994 describe reactors of the cold wall type. However, they do not consider the desirability of turbulent flow within the reactor, the role of a solid porous thermal insulation, and other critical parameters of the present invention, which will be discussed in detail hereinbelow.